In modern internal combustion engines, precisely attaining a designated fuel injection quantity is critical for obtaining optimal exhaust gas emission values. Moreover, in the case of multi-cylinder engines efforts are also directed at ensuring that as far as possible the same amount of fuel is injected into all the cylinders in order to achieve the quietest and most consistent engine operation possible. In this case the injection pattern on which the injected fuel quantity is based should be homogeneous, i.e. the same number of pilot, main and post injections per cylinder. If, for example, the injection pattern for each cylinder consists of a single main injection per combustion cycle, the aim is to ensure that for a predetermined operating point of the internal combustion engine not only the relative injection times (an injection time is normally specified as a function of the crank angle position of the piston), but also the injection quantities per injection are kept the same for all cylinders.
Achieving a predetermined injection quantity is made difficult due to manufacturing tolerances of individual components and controllers of the injection system. In particular, injectors can have manufacturing tolerances which result in different injection quantities even given identical operating parameters and ambient conditions. Furthermore, the components—the injectors in particular should once again be mentioned in this context—undergo a change in their operating characteristics in the course of their useful life and consequently in the effectively achieved injection quantities if no countermeasures are taken. The change in the operating characteristic of a component over the course of its lifetime is also referred to as drift.